One known type of feeding device comprises a support having a through opening and feed cylinders adjoining the opening, which feed cylinders are angularly distributed and which are individually arranged in a free end of a respective supporting arm and driven in rotation, and wherein the supporting arms in a supported end are journalled in the support on shafts extending in parallel with each other and pivotable about the shafts between a home position and a pivoted work position, and wherein the supporting arms are mutually connected to each other via a system of articulated links and by means of the links forced to pivot jointly about their respective shafts.
Feeding devices of this type are used in barking machines of rotation ring type of the kind comprising a stationary machine support and a rotor rotatably journalled in relation to the support and having a central hole for passing the logs. Usually one feeding device is located on the upstream side of the support for feeding the logs into the machine, while another corresponding feeding device is located on the downstream side of the support for outputting the barked log. A number of pivotable machining tools are mounted to the rotor, the machining tools being equipped with replaceable elements that can be pressed against the surface of the log in order to peel off the bark.
Feeding devices for barking machines have the function of feeding the logs in a quick and powerful way without the logs slipping in the contact with the feed cylinders. The feed cylinders are for this purpose typically arranged with friction increasing elements, for instance in the form of projecting pins or the like, at the envelope surface thereof. The feed cylinders must by the same cause be distinctly pressed against the logs but at the same time indulgently follow irregularities in the surface of logs having varying dimensions.
It is customary that the feeding speed through a feeding device at barking machines is in the range of a couple of meters per second or more. It is thereby realized that the feed cylinders and the links are exposed to high dynamical loads and rapid adjustment movements when a log enters the feeding device and leaving the feeding device, respectively.
A feeding device of this kind in known from the applicants earlier Swedish Patent having publication number SE 517517 C2. Distinguishing for this feeding device is that a holding down mechanism in the form of a compressible bellows is arranged between the support and a link that is part of the link system. The bellows is arranged to be compressed and expanded depending on the pivoting movement of the feed cylinders and has the function to generate a holding down force that secure the vital contact between the feed cylinders and the envelope surface of the log. A shock absorber having the function of damping the movement of the feed cylinders in connection with the log leaving the feed cylinders is configured to work between the support and a link that is part of the link system.
In the known feeding device considerable dynamical loads in the form of shocks and vibrations are transferred to the support in connection with the log entering and leaving the feeding device, respectively. These shocks and vibrations cause a great strain on the holders of the shock absorber and on the support.